1. Field of the Invention
The present invention relates to shock absorbers and, more particularly, to an improved shock absorber unit that is especially adapted for applications in which high damping forces occur.
2. The Prior Art
In the type of shock absorber disclosed in German Offenlegungsschrift 28 00 630, which is particularly intended for ski bindings, the piston unit comprises a piston member and a valve member, both of which are axially movable along the piston rod. The piston member and the valve member are biased in the same direction towards respective rest positions. A first flow passage is provided in the piston member, and a second flow passage is formed in part by a gap between the adjacent faces of the piston member and the valve member. The first and the second flow passages are connected in series; i.e., so that the damping fluid flows first through one and then the other of the two passages. When the piston rod is moved in a predetermined direction at low speed, fluid passes sequentially through the two passages from one working chamber to the other working chamber. When the speed is increased, the piston member is axially moved against the biasing force acting thereon due to the pressure drop across the first flow passage. The second flow passage is thereby reduced in flow cross-section, with the result that an increased pressure drop occurs across the second flow passage. This causes the valve member to be axially moved away from its rest position against the biasing action acting thereon, so that the second flow passage is again increased in cross-section.
The foregoing known construction being particularly useful for ski bindings is less adapted for applications in which high damping forces occur. In such applications, there is a risk of damage to the piston member due to high pressure of the damping fluid. Also, the piston member is likely to be expanded in the radial outward direction, so that increased friction occurs between the piston member and the cylinder. As a consequence, the damping characteristics of the unit can be undesirably altered. Moreover, it is at best difficult with such units to obtain certain desired damping characteristics, such as, for example, a damping characteristic according to which a low or even negligible damping force is provided at low velocity of movement of the piston rod, whereas upon the piston rod velocity exceeding a predetermined value, the damping force is suddenly increased to a considerably higher value which is subsequently gradually further increased upon further increase of the piston rod velocity.